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Chapter 29: Reflection and Refraction

29.1: Reflection
  • When a wave reaches the boundary between 2 media, some or all of the waves will reflect back into the original median
  • If all of the wave energy is reflected, then it is said to be totally reflected
  • If some of it passes into the 2nd median it is said to be partially reflected

29.2: Reflection
  • In two-dimensions, wave reflect off of a boundary at the same angle they arrive, but on a perpendicular imaginary line called the normal line
  • Angle the wave arrives at is referred to as the angle of incidence
  • Departing angle is referred to as the angle of reflection
  • Law of reflection:
    • Angle of incidence = angle of reflection

29.3: Mirrors
  • Virtual images are imaginary and occur behind an object
  • Virtual images always are the same size and distance behind the mirror as in front

29.4: Diffuse Reflection
  • Diffuse reflection occurs when a light ray reflects perpendicular to the surface, but reflects off a rough surface and scatters
  • The difference between rough and smooth surfaces depends of the wavelength of the wave striking the surface
    • If the bumps on the surface are small compared to the wavelength of the wave, than its a smooth surface and vice versa

29.5: Reflection of Sound
  • When sound bounces back off a surface with a noticable delay it is called an echo
  • If it bounces back and forth in a room it is referred to as reverberation
  • Sound waves have a much larger wavelength than light waves

29.6: Refraction
  • If a wave strikes a boundary between 2 different media at an angle, than the wave will be bent or refracted as it passes into th 2nd medium.
    • This occurs because the speed of thewave changes and the side of the wave that strikes the slower medium first will drag a little an cause the wave to turn in that direction

29.7: Refraction of Sound
  • Waves do not need a hard boundary between media in order to refract
  • They also bend if there is a gradual change in speed

29.8: Refraction of Light
  • When light rays move from a medium where light travels quickly such as air to one where light travels slower like water the light rays will refract toward the normal line.
  • If the light rays go in the opposite direction the rays will refract away from the normal line
  • Index of Refraction: index of refraction = speed of light in a vacuum/speed of light in the medium
  • Snell's Law:
ni sin Øi = ni sin Ør

29.9: Atmospheric Refraction
  • If the air right above the ground is warm but the air above that is cooler then light waves will curve upward
  • If you look in the distance this can cause you to see a mirage, when you see waht appears to be a reflecting surface such as water on the ground some distance away
  • It will also cause you to see the sun right before it goes down and right before it comes up which results in a five minute longer day

29.10: Dispersion in a Prism
  • Short wavelength light travels through some media at different speeds than longer wavelength light
  • The index of refraction varies for different colors of light
  • The blue end of the spectrum will refract more than the red end of the spectrum
  • This results in seeing a visible spectrum through a prism

29.11: The Rainbow
  • A spectrum is produced when light shines through a raindrops much like it does when it shines through a prism.

29.12: Total Internal Reflection
  • When light travels from a dense medium to a less dense medium it will speed up and refract away from the normal line.
  • The angle of incidence that makes the angle of refraction 90 degrees is called the critical angle.